1. Technical Field
The present invention relates generally to backup power systems for buildings, and more particularly to a backup power system that selectively provides power to particular circuits according to a power distribution priority profile, where power is applied sequentially to each particular circuit depending on the measured current loads of the particular circuits to which power has already been applied.
2. Background Art
Emergency or backup power systems start providing power to a building within a few seconds after electricity from utility (power) lines has been interrupted. In a typical backup power system configuration, power lines and a backup generator are connected to a transfer switch. When electricity from the power lines is interrupted, the transfer switch breaks the connection between the power lines and the main breaker of the building and establishes a connection between the generator and the main breaker of the building. The generator thereafter provides power to all the circuit lines in the building. In this configuration, the generator must either supply enough power (with an additional safety margin) to support the entire electrical load created by the building, or enough loads (e.g., lights, equipment, HVAC) must be manually shed so that the generator is not overloaded.
One way to avoid having to use a generator that is big enough to supply power to an entire building, or having to manually shed non-essential circuits and devices to avoid overloading the generator, is to connect a backup generator and only a single particular circuit line (i.e., from a particular single circuit breaker) to a transfer switch. When electricity from the power lines is interrupted, electricity stops flowing to the breaker box and consequently stops flowing to the one particular circuit line. The transfer switch breaks the connection between the one particular circuit line and the breaker box, and establishes a connection between the generator and the one particular circuit line. The generator thereafter provides power only to the devices (i.e., lights, electrical outlets, equipment, etc) connected to that circuit line. The problem with this configuration is that it is unlikely that all essential devices will be connected to the single circuit powered by the backup generator. Additionally, the single powered circuit is likely to include some non-essential devices that are powered by the backup generator. Powering such non-essential devices is a waste of valuable electricity that could be used to power essential devices connected to other circuits.
In another configuration, a backup generator supplies power to a dedicated circuit cabinet. All building circuits that are intended to be powered by the generator must be routed to this cabinet. In this configuration, adding or removing circuits from the group of circuits receiving backup power is very laborious and requires an electrician to re-route the circuits to/from the main breaker box.
Further, such backup power systems are not capable of providing power to circuits and devices that are initially essential (e.g., elevators containing people) and shedding those circuits and devices when they become non-essential after a short time (e.g., elevators after all the people have exited). Moreover, such backup power systems are not capable of prioritizing the circuits and devices to which power is supplied, i.e., provide power to the most critical circuits first, then to the less critical circuits if power is available. Current backup power systems simply supply power to the circuits to which they are connected, and individual devices must be shed manually. Moreover, the circuits and devices that are powered by such backup systems are predetermined and unalterable, and cannot be adjusted based on some event.
Consequently, there exists a need for a backup power system that is capable of providing power to an entire building, prioritizing the supply of power to essential circuits and devices, and automatically shedding all non-essential circuits and devices as available power dictates.